1. Field of the Invention
The present invention relates to a lens drive apparatus, which drives a lens.
2. Description of Related Art
A vehicle drive assist system, which includes a onboard video camera to monitor a front side or a rear side of a vehicle, has been marketed. In this system, an image, which is captured by the onboard camera, is displayed on a monitor provided in a passenger compartment of the vehicle. In one previously known system, a stereo camera is used as the above video camera to measure a distance relative an obstacle. In another system, the distance measurement function of the above system is implemented as a scanning laser distance meter. In the scanning laser distance meter, a laser beam is scanned, i.e., swung and is transmitted through a transmission window toward an obstacle. The reflected light, which is reflected from the obstacle, is detected, and the distance to the obstacle is computed based on the detected light.
Japanese Unexamined Patent Publication No. 10-96624 discloses one apparatus that scans the laser beam by swinging a mirror. Instead of swinging the mirror, a lens may be swung or move to scan, i.e., to swing the laser beam. In such a case, the mechanism recited in Japanese Patent No. 3317997 (corresponding to U.S. Pat. No. 5,303,089) or in Japanese Unexamined Patent Publication No. 10-123252 may be used to swing or move the transmitter lens. In the mechanism recited in Japanese Patent No. 3317997, a bobbin, which holds a lens, is supported by leaf springs, thereby enabling the simplified mechanism. In the mechanism recited in Japanese Unexamined Patent Publication No. 10-123252, multiple coil springs are used to support a lens. The coil springs extend in a direction of an optical axis. The lens is driven by an actuator. This mechanism enables wide range scanning at low costs and high reliability.
The apparatus recited in Japanese Patent No. 3317997 is intended to be used in scanning of an optical disc, and the lens is moved in a single direction that is parallel to the optical axis of the lens. However, in the distance meter, which measured the distance by scanning the laser beam, the lens needs to be moved in the plane that is perpendicular to the optical axis. More specifically, the lens needs to be moved in a first direction, which is perpendicular to the optical axis, and in a second direction, which is perpendicular to the first direction. At this time, unlike Japanese Patent No. 3317997, the lens is placed in a plane, along which the leaf springs of the bobbin extend. In the apparatus recited in Japanese Patent No. 3317997, a yoke is made by bending a single metal plate, and another yoke is placed at an opening end of this yoke. When the lens is placed at the opening end of the yoke, there would not be a problem. However, when the lens is placed in the plane, along which the leaf springs of the bobbin extend, it is difficult to place the magnets, the coils and the yokes without causing interferences with the lens and the optical axis, so that these components need to be placed in remaining limited spaces. When the yokes are formed integrally, the assembling is not easy.
Furthermore, the distance meter, which scans the laser beam, is often installed in the vehicle. In the case of the vehicle, durability of the distance meter needs to be higher than that of domestic appliances. However, the metal plate yokes alone cannot provide the sufficient rigidity, thereby resulting in the low durability of the distance meter.
In the apparatus disclosed in Japanese Unexamined Patent Publication No. 10-123252, the assembling of the lens drive mechanism may not be troublesome. However, the support structure, which supports the lens by the coil springs, is not good enough in terms of the durability. Also, in the case where the apparatus is installed in the vehicle, the countermeasures against the vibration are not good enough.